1. Field of the Invention
The present invention relates to a p-type semiconductor substance having a thermoelectric converting property for use in a thermoelectric converting module, and more particularly to a p-type thermoelectric converting substance mainly consisting of a substance represented by a chemical formula of CoSb.sub.3 and a small amount of Sn or Ge serving as an additive for controlling the conductivity of the substance to p-type. The present invention also relates to a method of manufacturing such a thermoelectric converting substance.
2. Description of the Related Art
Heretofore, there have been proposed telluric compound such as Bi.sub.2 Te.sub.3, Bi.sub.2 Sb.sub.8 Te.sub.15 and BiTe.sub.2 Se as a thermoelectric converting substance. Among antimony compounds generally expressed as TSb.sub.3 (T: Co, Ir, Ru), CoSb.sub.3 has been known as the thermoelectric converting substance. CoSb.sub.3 thermoelectric converting substance can be used in a temperature range up to about 600.degree. C.
The above mentioned telluric compounds generally expressed by Bi-Te have a relatively high performance index Z of about 3.times.10.sup.-3 [l/k] at room temperature, but the performance index is decreased in a temperature range higher than 300.degree. C. Furthermore, the thermoelectric converting substance mainly consisting of the above mentioned telluric compound has a low melting point and a poor chemical stability, and moreover its thermoelectric converting property might be largely varied depending upon a deviation in composition.
Among the Sb base compounds expressed by TSb.sub.3 (T: Co, Ir, Ru), CoSb.sub.3 can operate satisfactorily over a much wider temperature range than Bi--Ti series compounds. Such thermoelectric converting compound semiconductor CoSb.sub.3 has been described in L. D. Dudkin and N. Kh. Abrikosov, Sov. Phys. Solid State, 1(1959), pp. 126-133. In such a compound semiconductor, however, there is a problem in obtaining a thermoelectric converting substance having a p-type conductivity. That is to say, stoichiometric CoSb.sub.3 having no additive shows p-conductivity type, but when an additive is not added, the conductivity of the substance could not be controlled due to the influence of non-purity of raw materials and it is difficult to attain a stable thermoelectric converting property. Moreover, the control of the conductivity type could not be performed effectively.
In addition to the problem of the non-purity of raw materials, there is a problem in that the composition of the substance is inevitably changed during the manufacturing process. Particularly, when a lack of Sb occurs in the stoichiometric composition, the conductivity type might be inverted and the finally obtained thermoelectric converting substance becomes n-type.
Due to the above explained reasons, in order to obtain p-type CoSb.sub.3 showing high and stable thermoelectric conversion properties, it is necessary to dope a raw material of CoSb.sub.3 with impurities controlling the conductivity type to the p-type, and further it is also necessary to remove the variation in composition during the manufacturing process.